function showCheck(a) {
  var c = document.getElementById('myCanvas')
  var ctx = c.getContext('2d')
  ctx.clearRect(0, 0, 1000, 1000)
  ctx.font = "80px 'Microsoft Yahei'"
  ctx.fillText(a, 0, 100)
  ctx.fillStyle = 'rgba(255,255,255,.9)'
}
